1. Field of the Invention
The present invention relates to an apparatus capable of non-destructively evaluating the characteristics of a measurement target by irradiating a laser beam to the measurement target, and more particularly to a multiple-beam path laser optical system using a multiple beam reflector, capable of generating a multiple laser beam and appropriately irradiating the multiple-laser beam to a measurement target.
2. Description of the Related Art
Defect inspection used in the fabrication process of a semiconductor and the like requires detecting fine defects, measuring the dimension of the detected detect with the high degree of precision, non-destructively inspecting a sample (for example, without chemically changing the specimen), actually obtaining predetermined inspection results with respect to, for example the number, the positions, the dimension, and the type of inspected defects when the same specimen is inspected, and inspecting a plurality of specimens within a predetermined period of time.
When a non-destructive inspection is performed among them to evaluate the characteristics of a thin film or a semiconductor chip, a laser optical system has been recently used.
Regarding a method and an apparatus for inspecting the internal characteristic of an object using the laser in a non-contact way, various patents are suggested by several inventors.
For example, referring to FIG. 1, a laser beam generated from alight source part 10 is irradiated to a mirror 30 and a specimen 40 by a beam splitter 20, and the irradiated laser beam is analyzed by a control part 50 based on an interference pattern.
However, in the conventional optical system, the intensity of light and the polarizing state may be varied due to environmental changes, such as heating, a surrounding temperature, or fine vibration, resulting from the use of the laser for a long time.
Accordingly, when two specimens, which are different from each other, are inspected, the two specimens must be sequentially and independently inspected. Therefore, it is difficult to inspect the two specimens under mutually different conditions.
In other words, since a conventional laser optical system has a single optical path, the difference between intensities of laser beams irradiated to the first specimen and the next specimen may be made due to surrounding influences when the specimens are continuously inspected. Accordingly, the significant measurement error may be made between the specimens.
As a prior art, there is Korean Unexamined Patent Publication No. 10-2011-0120110 entitled “Laser beam apparatus which uses more than 2 laser optical system and method thereof”.